1. Field of the Invention
The present invention relates generally to a device and method for ultrasonic intraluminal imaging. More particularly, an intravascular catheter is provided for imaging a portion of a blood vessel in a plane extending axially from the tip of the catheter. The catheter system of the present invention may also include an additional diagnostic or interventional work element for use in conjunction with the imaging element.
2. Description of the Background Art
Arteriosclerosis, also known as atherosclerosis, is a common human ailment arising from the deposition of fatty-like substances, referred to as atheromas or plaque, on the walls of blood vessels. Such deposits occur in both peripheral blood vessels that feed the limbs of the body and the coronary vessels which feed the heart. When the deposits accumulate in localized regions of a blood vessel, stenosis, or narrowing of the vascular channel, occurs. Blood flow is restricted and the person's health is at serious risk.
Numerous approaches for reducing and removing such vascular deposits have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of atheroma, atherectomy where a blade or cutting bit is used to sever and remove the atheroma, spark gap reduction in which an electrical spark burns through the plaque and laser angioplasty where laser energy is used to ablate at least a portion of the atheroma.
A major difficulty in using such devices is obtaining images and information on the region of the blood vessel to be treated. To overcome this difficulty, several techniques have been proposed for intraluminal imaging of vascular vessels. Catheters incorporating ultrasonic transducers for imaging are disclosed in U.S. Pat. Nos. 4,794,931; 5,000,185; 5,049,130; and 5,024,234. However, these catheters scan in a plane normal to the catheter axis. While such catheters are very useful for examining deposits adjacent to their distal tips, they are generally incapable of imaging the vessel downstream of the catheter.
Such downstream viewing would be useful in a variety of circumstances. For example, it would provide a visual determination of whether there is a channel through which a guide wire or catheter may be passed. Moreover, downstream viewing could provide information to help the physician to determine which type of intravascular device would be most suitable for reducing the stenosis. Finally, downstream viewing can be invaluable as an aid in directing and using interventional and diagnostic devices and avoiding accidental penetration of the vessel wall.
U.S. Pat. No. 4,576,177 to Webster describes a laser catheter having an ultrasonic transducer mounted at a fixed angle of inclination to the catheter tip. The transducer is not movable with respect to the catheter tip however, and is therefore only capable of imaging along a line fixed with respect to the catheter body.
U.S. Pat. No. 4,587,972 to Morantte discloses a catheter apparatus having an array of transducing elements. The elements are sequentially excited to obtain an image distal to the catheter. Such phased array devices are very complicated and therefore costly to fabricate. Their resolution and ability to steer the beam through a wide range of angles are limited by the number of elements provided.
It would be desirable to provide a catheter apparatus capable of imaging a blood vessel downstream of the catheter itself. It would be desirable if such a catheter were capable of scanning a region of the blood vessel in a plane located forward of the catheter. Such a catheter should be of relatively simple design to allow for compact construction and reliability of use. Additionally, it would be desirable to combine such a forward viewing catheter with an additional working element to provide the catheter system with a further diagnostic or interventional capability.